In earth boring operations involving use of earth boring percussion bits, it is desirable to provide a technique of keeping a bit head connected to a piston case even though the bit head has broken. If the bit head becomes detached from the piston case and is left in the hole, it is necessary to retrieve the bit head from the hole, which can be costly and difficult, and, if retrieval is not possible, it may be necessary to abandon the hole. Various systems have been devised for retaining a broken bit head relative to a piston case. Several of these system are disclosed in U.S. Pat. Nos. 5,065,827, 5,647,447, and 6,070,678, the disclosures of which are incorporated by reference. It is desirable to provide a bit head retention system that will retain a broken bit head relative to a piston case during earth boring operations.
In accordance with an aspect of the present invention, a bit head retaining system includes a bit head having an upper end and a working face, a driver sub having an internal opening in which the upper end of the bit head is axially movable, and a retention sleeve having an internal opening in which at least a portion of the bit head above the working face and at least a portion of the driver sub are disposed, the retention sleeve being axially immovable relative to the bit head.
In accordance with another aspect of the present invention, a bit head retaining system includes a bit head having an upper end and a working face, and a retention sleeve adapted to be connected to an end of a drill casing and having an internal opening in which at least a portion of the bit head above the working face is disposed, the bit head being secured to the retention sleeve so as to be axially immovable relative to the retention sleeve.
In accordance with yet another aspect of the present invention, a method of installing a bit head in a percussion drill includes inserting an upper end of a bit head into an internal axial opening at a first end of a driver sub, sliding a retention sleeve over a second end of the driver sub until an internal recess in the retention sleeve aligns with an external recess in the bit head, securing the bit head relative to the retention sleeve with a retention member disposed in the external recess in the bit head and in the internal recess in the retention sleeve, and attaching the second end of the driver sub to a piston case.